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  1. #1

    Hmm Rooftop Luxaire units - Increasing Condenser Fan HP (RPM)

    I have 1/2 hp condenser fan motors on my rooftop units, rpm=1075. To increase heat exchange; is it a good recommendation to increase the motor hp to 3/4 with an increased rpm ~1600. Do I need to worry about fan pitch? Please advise.

  2. #2
    Join Date
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    May I ask why you would want to do that?

  3. #3
    its just a thought for a resturant. The units are right sized, the coils are clean and filters changed, pressures good, etc. Althought there is a high heat load right now in the south...thus in the restuarant, I was looking for a way to "get move heat out", if that makes sense. If the units runs longer to remove the heat, an increase fan speed could possibly remove more heat and and reduce electrical cost...its just a theory.

  4. #4
    Join Date
    Aug 2006
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    Mixing oil and fire with a big spoon.
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    4,269
    ALL THINGS BEING EQUAL...

    taking a 0.5 HP fan @ 1,075 RPM and installing a 1,550 RPM motor, will cost you 1.5 HP. when you change speeds up, you go way up on HP. your CFM will only change about 44% higher. using a higher HP motor in this case will also potentially cause motor overheating...your HP is 300% of the old motor but it is only 44% of the extra airflow. also keep in mind that the original wiring was only designed for a 0.5 HP motor. all of this is assuming that you are also keeping the current fan blade and that it needs a 0.5 HP motor.

    i would focus on condensor cleanliness first. then i would focus on making sure that the current fan blade meets the specs of the original. moving more air will help lower head pressures and this will help remove more heat and save money on the compressor side, but at a cost to the fan motor side. there is also the issue of TXV or orifice/cap tube. if it is a TXV then you can move more air without much problem...but if it is an orifice/cap tube, your pressures are going to be off. also consider that more air flow in low ambient conditions may cause more problems.

    good luck.
    my 1st time jumping out of a plane...http://youtu.be/Kv38G0MHsGo

  5. #5
    Join Date
    Jul 2007
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    Tulsa, OK
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    975
    If'in it aint broke, fix it? Add water hose flow to the condenser coils and after 3 months you'll have calcium deposits clogging the coils and causing hot spots. But hey it removed more heat and lowered your bill by $xxx.xx. Now that really is great except compared to another ten times more $ to get back to normal with replaced condenser coils. Over engineering causes problems bigtime.

  6. #6
    thanks for the information!!! I was thinking that the "runtime" saving maybe offset with increased amperage of the larger HP motor. However, you shread much more light on the subject. Can you recommend reading material where I can read up more on this subject?

  7. #7
    Join Date
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    most of the time in the Philippines
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    Quote Originally Posted by morningstar View Post
    thanks for the information!!! I was thinking that the "runtime" saving maybe offset with increased amperage of the larger HP motor. However, you shread much more light on the subject. Can you recommend reading material where I can read up more on this subject?
    Quote Originally Posted by morningstar View Post
    thanks for the information!!! I was thinking that the "runtime" saving maybe offset with increased amperage of the larger HP motor. However, you shread much more light on the subject. Can you recommend reading material where I can read up more on this subject?
    The fan laws [relationships among speed, horsepower, cfm, and static pressure is what you're looking for. Fasco puts out a little booklet called "fasco facts" it's in there. www.fasco.com All techs need this booklet. Fasco wholesalers should have it otherwise check the site. Update- the site is being remodeled, you can't download the booklet. Call the number on your screen, see they can help you.
    1-800-325-8313

    Also, go to www.lauparts.com Click on literature, print out all the pdf files on replacement blowers and fan blades, put them in a binder and put the binder on the truck. Very handy to have. Like, for example, when one of my techs threw away a rusted blower housing assembly out of a pkg unit. After Carrier said sorry, no longer availbale, he comes to me and says oops. I showed him how to start from scratch and select a new blower section, drive pulley, and belt size. Like the commercial says, it's in there. It saved our butts on that job, plus the tech learned something.

  8. #8

    Smile

    I really appreciate the information...Thanks everyone!!!

  9. #9
    Join Date
    Dec 2006
    Location
    Washington, DC
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    509
    Quote Originally Posted by morningstar View Post
    If the units runs longer to remove the heat, an increase fan speed could possibly remove more heat and and reduce electrical cost...its just a theory.
    The manufacture designed the air flow across the condenser coil. Not sure how old the unit is, but newer equipment is design for the best efficiency [IE: airflow versus coil surface].

    If you start moving too much air across the coil, you could potentially not get the best heat exchange and cause the unit to run longer.

    I am not an engineer, but changing the airflow could also cause other issues with the operation of the unit. As the compressor size, refrigerant charge, condenser fan motor size, fan blade, etc where all calculated in the design of the equipment.

    I would research everything thoroughly before changing the manufacture’s design. It could end up costing more in electrical costs, plus other problems.

    If electrical costs are an issue. You would probably benefit the customer more in replacing the older equipment with new efficient ones. Doing this will not only save on electrical consumption, it will reduce repairs costs as the equipment is newer.
    Quote Originally Posted by Qui-Gon Jinn (Star Wars Episode 1)
    "The ablilty to speak does not make you intelligent!"

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